Diethyl toluene diamine (DETDA) is currently being used on a large commercial scale as a chain extender for the production of polyurethane elastomer moldings via the RIM process. Formulations utilizing DETDA allow for fast demold times and high productivity because of the high reactivity of DETDA with aromatic isocyanates. However, the concentration of DETDA that can be used in a formulation is limited by the high reactivity of the DETDA. In fact, in commercial applications, concentrations higher than about 23 to 25 percent by weight (based on the total weight of all the active hydrogen containing components in the reaction mixture) cause such fast gelation that even simple molds cannot be filled uniformly. While increasing the DETDA concentration will result in an increase in flexural modulus (or stiffness), the resultant molded part is also unacceptably brittle.
The formulations based on DETDA as a chain extender are therefore restricted to the lower flexural modulus range (i.e., less than about 70,000 psi at room temperature). As is known in the art, flexural modulus could be raised through the use of a co-chain extender, such as ethylene glycol or 1,4-butane diol with DETDA. However, when such co-chain extenders are used the thermal properties of the molded part such as heat sag and flexural modulus at high or low temperatures are generally adversely affected.
It is therefore an object of the present invention to provide higher flexural modulus polyurethane elastomer moldings. It is a further object of the invention to provide such formulations which give acceptable flowability in complicated molds, and which are not brittle at or following demold.
The use of DETDA in the production of polyurethane elastomer moldings has been described in U.S. Pat. Nos. 4,218,543, 4,288,564, 4,298,701 and 4,296,212; U.S. Application Ser. No. 288,222, filed July 29, 1981 and now U.S. Pat. No. 4,379,105; and British Pat. No. 1,534,258. Furthermore, each of these references do broadly suggest the use of 1,3,5-triethyl-2,6-diamino benzene. In the '543 patent, note column 10, lines 1 and 2, and Claims 4 and 18; in the '564 patent, note column 8, line 22; in the '701 patent, note column 7, line 20; in the '212 patent, note column 4, line 54; in the British patent, note page 7, line 3; and in the U.S. application, note page 17, line 32 and Claim 2.
Finally, the use of both DETDA and 1,3,5-triethyl-2,6-diamino benzene in a prepolymer process has been described in U.S. Pat. No. 3,428,610 (note particularly, column 4, lines 22-23; column 5, lines 7 and 8; and Example 9H).